The present invention relates to an illuminating device for an electrophotographic copier, particularly a color copier.
An illuminating device which is installed in a color copier generally includes color separating filters of different colors. Because each of the filters has a particular spectral transmission characteristic, the amount of exposure has to be varied from one color to another in order that exposure in the respective colors may be effected based on the difference in spectral transmission characteristics. To meet this requirement, it has been customary to selectively use different kinds of halogen lamps, fluorescent lamps and other light sources each being assigned to a respective one of the colors, or to vary voltage which is applied to a light source color by color.
However, a problem with the multiple light source scheme is that it needs a great number of structural units which increase the cost, while failing to attain sufficient reliability. Poor illumination efficiency due to limited efficiency of a reflector is another problem. On the other hand, the variable voltage scheme has a drawback that a change in voltage is accompanied by a change in color temperature and, therefore, the range of light adjustment available is quite limited.